Electron tube power output circuit for low impedance loads



Nov. 22, 1949 E. K. STODOLA 2,488,567 ELECTRON TUBE POWER OUTPUT CIRCUIT FOR LOW IMPEDANCE LOADS Filed June 16, 1945 FIG. 3. INPUT I 5 1 BALANCED I AMPLIFIER B+IOO a+aoo REGULAR CATHODE FOLLOWER 'OR IMPROVED OUTPUT SYSTEM WITH NO LOAD- IMPROVED CIRCUIT WITH .05 MED. -..C CONDENSER LOAD. l

\ INVENTOR. EDWIN K. STODOLA \'='REGULAR CATHODE FOLLOWER WITH .OSMED. CONDENSER LOAD. BY l 4 5414 2o MICROSECOND PULSE ATTORNEY Patented Nov. 22, 1949 ELECTRON TUBE POWER OUTPUT CIRCUIT FoR LOW IMPEDANCE LOADS Edwin K. Stodola, Neptune, N. J.

Application June 1.6, 1945, Serial No. 599,944 3 Claims. (01.179-171) (Granted under the act of March 3, 1883, as

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

My invention relates to electron tube networks andmore particularly to networks for driving loads of low impedance. It is especially applicable for driving reactive loads in the form of large capacities.

One type of circuit to which my invention is especially applicable is the conventional cathode follower circuit, particularly when such a circuit is used for driving a reactive load such as a relatively high capacity which may be shunted by a high resistance, with a signal in the form of asharp-sided pulse. In conventional circuits of this type, the positive-going edge of the pulse will be relatively sharply reproduced while the negative-going edge will be distorted.

It is a principal object of my invention to provide an electron tube network for driving such loads Without the need for maintaining the large steady currents which are usually necessary for providing rapid response in the output circuit to changes in the input circuit.

-It is a further object of my invention to provide an electron tube network for driving capacitative loads with relatively sharply varying signals with minimum distortion thereof.

'The novel features of my invention are set forth in the appended claims, but the organiza tion, operation, advantages, and further objects of my invention may best be understood by the following description taken in connection with the accompanying drawings, wherein similar components are indicated by -like reference numerals, and wherein:

Figure 1 is a'schematic circuit diagram conventional cathode follower circuit;

' Figure 2 is a schematic circuit diagram of one embodiment of my invention;

Figure 3 is a block diagram of a furtheremoia . bodiment of my invention;

Figure 4 is a schematic circuit diagram corresponding to the block diagram of Fig. 3; and

Figure 5 is a typical .oscillogram showing the improvement in performance which is obtained by the use Of my invention.

' Reference is now made to Fig. 1, which'shows a conventional cathode follower circuit feeding a capacity load C. V1 is a conventional triode, C1 is the input coupling condenser, and R1 the load resistor which is regarded as separate from the capacitative output load represented by the capacitor 0. E1 is the D.C. source provided with amended April 30, 1928; 370 O. G. 757) a tap to which input resistor Rz'is connected to provide grid bias for establishing the quiescent operating point of V1 at the proper level. As the input pulse goes positive the condenser C is.

rapidly charged through the relatively low resistance electron path in the tube, and, if the voltage across C tends to rise less rapidly than the grid voltage, the tube conducts more heavily and tends to make the output voltage rise rapidly. On the other hand, when the negative-going portion, or fall of the pulse starts, if the. voltage fully large tubes and currents to obtain a given performance. 7

In accordance with my invention, one embodiment of which is illustrated in Fig. 2, this difficulty is overcome by substituting for loadresistor R1 of Fig. 1, a tube V2 whose control element is driven in a sense which is opposite to that of V1. R2 is returned to an intermediate voltage tapas in the case of Fig. l to establish a, quiescent operating point, and the grid of V2 is established at a suitable negative potential through R3 and D.-C. source E2. The load C is connected between a point on source E1, in this case the negative terminal, and the junction-of tubes V1 and V2.

Two voltages varying in opposite sense for controlling tubes V1 and V2 are derived from a paraphase amplifier V3 having a plate resistor R4 and a cathode resistor R5. The voltages across the respective resistors vary in opposite sense, and are respectively applied to tubes V1 and V2 through coupling condensers C1 and C2.

The input signal is applied to V3 through a coupling condenser C3 and an input resistor Re, which is returned to a tap on E1 to establish the operating point. Any other means for obtaining oppositely varying voltages, which need not necessarily be equal, may be used.

' The circuit in Fig. 2 can beiurther improved by. providing additional drive on V2 if the voltage across C tends to lag behind the grid voltage. This is accomplished by the use of a feedback circuit, an example of which is shown in Fig. 3, wherein the output is balanced against the input resistors in Re and R7 and the voltage appearing at the junction is applied to an amplifier E having a balanced, push-pull output which, in turn, is applied to the grids of output tubes V1 and V2 in proper phase. Thus, if the output voltage variations tend to lag the input voltage variations, a greater actuating voltage is applied to the input of the balanced amplifier tending more; strongly to make such output voltage variations match (in opposite sense) said input voltage additional amplification, R12 being its plate load.

resistor and R9 its cathode bias resistor. R10 is the input resistor and C4 the input coupling:

capacitor for the added stage, and C5 the input blocking condenser for the whole network.

Figure 5 shows sketches of oscillograms of pulses obtained in the circuit of Figs. 1 and 4. The input pulse for both circuits, except for polarity differences, is shown by solid curve A, which also shows the output pulse for both circuits providing there is no load on the network or said load is purely resistive. However, when the conventional cathode follower in Fig. 1 is loaded by a capacity, the pulse, and particularly the trailing edge of the pulse, is seriously distorted, as shown by dotted curve B, while with the novel system of Fig. 4, the distortion is only slight, as shown by the dotted curve C. The total steady plate current required by the two systems is approximately the same in each case.

Although the advantages of the above invention have been described with particular reference to capacitive loads, it should be understood that it is useful in connection with resistive or other loads where it is desirable that the output network have low internal impedance.

While there has been described what is at present considered a preferred embodiment of the invention, it will be obvious to those skilled in the circuit having substantially no impedance to said.

signals to the positive terminal of a source of direct current, a second tube having a cathode,

plate, and grid, a connection from the cathode of the first tube to the plate of the second tube,

the cathode of the second tube being connected through a circuit having substantially no impedance to said signals to the negative terminal of said source of direct current, a load connectedbetween a point on said direct current source and said connection, means for biasing said grids, an input circuit, first and second resistors connected in series between the input circuit and the said connection, and amplifier means having its input connected to the junction of said two resistors and having oppositely-phased outputs which are connected respectively to said grids in such manner that the signal at said connection is opposite in polarity to the signal at said input circuit, whereby distortion of pulse signals is minimized.

2. An electron tube network for translating signals including a first tube having a cathode, plate, and grid, said plate being connected through a circuit having substantially no impedance to said signals to the positive terminal of a source of direct current, a second tube having a cathode, plate, and grid, a connection from the cathode of the first tube to the plate of the second tube, the cathode of the second tube being connected through a circuit having substantially no impedance to said signals to the negative terminal of said source of direct current, a capacitative load connected between a point on said direct current source and said connection, an input circuit, first and second impedances connected in series between the input circuit and the said connection, and amplifier means having its input connected to the junction of said two impedances and having oppositely-phased outputs which are connected respectively to said grids in such manner that the signal at said connection is opposite in polarity to the signal at said input circuit, whereby distortion of pulse signals is minimized.

3. An electron tube network for translating signals including a first tube having a cathode, plate, and grid, said plate being connected through a circuit having substantially no impedance to said signals to the positive terminal of a source of direct current, a second tube having a cathode, plate, and grid, a connection from the cathode of the first tube to the plate of the second tube, the cathode. of the second tube being connected through a circuit having substantially no impedance to said signals to the negative terminal of said source of direct current, a capacitative load connected between a point on said direct current source and said connection, an input circuit, an impedance connected between the input circuit and: the said connection, and amplifier means having its input connected to an intermediate point on said impedance and having oppositelyphased outputs which are connected respectively to said grids in such manner that the signal at said connection is opposite in polarity to the signal at; said input circuit, whereby distortion of pulse signals is minimized.

EDWIN K. STODOLA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,033,136 Ferrell Mar. 10, 1936 2,226,459 Bingley Dec. 24, 1940 2,281,618 Riddle May 5, 1942 2,358,428 White Sept. 19, 1944 2,411,706 Berkoff Nov. 26, 1946 2,431,973 White Dec. 2, 1947 FOREIGN PATENTS Number Country Date 412,182 Great Britain June 19, 1934 

